This is a competing continuation of a Bioengineering Research Partnership (BRP) grant focusing on the molecular mechanisms of traumatic brain injury (TBI). Our work in the last phase points out a potentially critical receptor - the calcium permeable AMPA receptor (CP-AMPAR) - that appears in neurons after mechanical injury and plays a key role in neuronal death. In the final phase of this BRP, we define the mechanisms regulating the appearance of CP-AMPARs (Aim 1), determine when CP-AMPAR activation leads to neuronal death (Aim 2), and develop therapies for reversing neuronal death initiated by CP- AMPARs (Aim 3). Our therapeutic approaches include strategies we can test immediately with available compounds, as well as new therapies developed with unique technologies to target key molecular events that lead to neuronal death. Our overlying hypotheses are (a) CP-AMPARs increase following injury due a change in the translation of AMPAR subunits, a change in the editing of GluR2 mRNA, and an ERK mediated insertion of GluR1 homomeric AMPARs. (b) Immediate or delayed inhibition of calcium permeable AMPARs reduce neuronal death after mechanical injury, and their effect is enhanced restoring G^luR2 editing (calpain inhibition) or inhibiting ERK phosphorylation, (c) Restoring ADAR2 editing activity of GluR2 mRNA, limiting the GluR2 synthesis, and interrupting Elk-1 signaling selectively in dendrites are effective delayed strategies to improve neuronal survival after injury. . We integrate the collective expertise of the BRP labs to test these hypotheses across the subcellular, cellular and organ scale. We evaluate transcription factor (Elk-1) signaling and the synthesis/regulation of CP- AMPAR subunits within individual dendrites after injury, measure changes in RNA editing and transcription within individual neurons and in slice culture, and test newly developed therapies in animal models of TBI. Relevance: This work studies factors that cause cell death after traumatic brain injury. The investigators test treatments to reduce neuronal death using commercially available compounds, and design new molecules that may be even more effective in reducing cell death. Both treatment approaches are tested for their effectiveness if given either immediately or several hours after injury, which is critical to know if these will be used clinically in the future.